Modern computers are based on binary logic, in which any given bit of information is in one of two exclusive states, typically designated as 0 and 1. Binary coding schemes have long been used to allow marking and recognition of objects; early computers used punched paper cards to store information, with the holes being read by means of electrical, mechanical or optical sensing.
A more contemporary example of the use of binary coding with remote sensing is described by Weber in U.S. Pat. No. 4,355,300, where a series of sensing elements reads conductive indicia in fixed positions upon a substrate, each sensing position signaling the presence or absence of an indicium and the resulting binary bits forming a complete code value. U.S. Pat. No. 5,159,181, by Bartels et al., describes a similar sensing system wherein a single sensor moves past a series of multiple sensing locations on a substrate, or multiple sensing locations on a substrate are moved past a single sensor, with each sensing location producing a indication of one of two states, resulting in a binary code. The Bartels et al. system requires a means to move the sensor and the substrate relative to one another, and complex temporal analysis of the sensor waveform to extract the values corresponding to each sensing location. These exemplary systems rely on binary encoding to convey a value, thus reducing the range of code values that can be encoded by a given number of sensors or sensing locations.
A number of systems have been described for taking simultaneous or serial measurements from a series of sensors and analyzing the pattern of measurements to deduce information about an object in the vicinity of the sensors. U.S. Pat. No. 5,374,787 by Miller et al. describes the use of a parallel series of touch sensors, where the response of each sensor is compared to the no-touch condition, and the centroid of the response curve is determined to detect the position of touch along the series of sensors. U.S. Pat. No. 4,999,462 by Purcell describes a collinear series of triangular sensors and a circular excitor, where the pattern of response of the sensors is compared with a look up table to determine the location of the cursor. These exemplary systems use multiple sensor levels, but serve only to determine the location but not the identity of an object.
Commercially available MICR (magnetic ink character recognition) systems read indicia encoded on checks using magnetic ink and a specific character set designed so that a magnetic sensor produces a temporal signal pattern unique to each character when the check is moved past the sensor. The temporal signals are converted into the corresponding digits to determine the coded number/character sequence. While this system encodes more than one value per sensed position, the system requires special inks and printers to encode the numerical value on the substrate, a means to move the check past the sensor to create the signal, and sophisticated temporal processing and pattern recognition to decode the value.
The teachings of each of the above-listed citations (which does not itself incorporate essential material by reference) are herein incorporated by reference. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention.
What is required is a system that overcomes the limitations of binary encoding to increase the range of values that can be encoded in with a fixed number of sensing locations on a substrate, but does not require complex and expensive means for moving the sensor and substrate relative to one another, nor complex temporal processing circuitry to extract the encoded value from the sensor readings.